Yeah.......in your irrigation/imaging question the problem with available commercial vertical aerial photography is the scale.......
Space based commercial imaging using scanning technology is fine for land mass but shy on detail........
Vertical photography from aircraft is usually available from your "county land planning" office.......These are shot from the bottom of the aircraft.....in overlapping views......Actual film....9" x 9" negatives........sometimes from an altitude of 10,000'......still small scale but since it's a single image there's more detail available.....
These are the images to consider for your request.....Check with planning........the actual vendor is usually noted on the prints.........These over-flights are generally annual events.......contacting the provider(if available) will allow the most flexibility in purchasing what you want...........
Now in "hind-sight"......If you really want(ed) to see the difference with the irrigation........Hire a Commercial Aerial Photographer to shot the site before and after the changes........There's no comparison to the level of detail in a custom oblique aerial photograph of the property.........
For a web-directory of 'Some' Aerial Photographers Try:
http://www.cloudhopper.com/aerial_state.htm
And you're welcome to contact me directly with your location for a more personal response ............doug :-)